The present invention relates to a stator with a uniform structure capable of being applied to high-pressure compressors in gas turbine engines.
The structure of the rotor and stator in gas turbine engines is often cooled or ventilated by air drawn from the flow that runs through the machine. Double ventilation may even be used in conjunction with two sources of drawn-off air or a downstream section of the stator and rotor can be ventilated after the stator and rotor have been initially ventilated further upstream. The air that is drawn off for the downstream ventilation comes from a section of the machine where it has already been compressed, thereby heating it to a higher temperature than the upstream ventilation air. The usual problem of obtaining a correct setting of the diameters of the stator and rotor in order to avoid an excessive increase in play at the end of the blades, which would increase the air leaks and loss of efficiency or, on the contrary, would eliminate the play and cause the rotor blades to rub against the stator, then becomes extremely difficult to solve due to the uneven conditions of ventilation. These conditions create different temperatures and thermal expansions between the sections that are subjected respectively to the two sources of ventilation. Another problem arises out of the fact that the various sections of the machine, including those that are located close to the compressor, are heated to different temperatures depending on whether they are near the ventilation air or the hotter air of the flow jet. This results in unequal expansions, distortions and stresses within the stator. Variations in temperature occur more quickly in certain zones such that the above problems can become more or less serious locally during phases of speed change. No known stator structure is completely satisfactory under these conditions.
The invention consists in dividing the stator structure on either side of the junction of the ventilation zones and of constructing the stator differently between the sections subjected to upstream ventilation and those subjected to downstream ventilation. In its most general form the invention consists in a compressor stator provided with upstream ventilation and downstream ventilation of air that is hotter than the upstream ventilation. It also comprises a shroud surrounding a gas flow jet, characterized in that it comprises a first section of shroud, which is subjected to the upstream ventilation, with an unbroken annular construction around a circumference and that is made of a first material, and a second section of shroud, which is subjected to the downstream ventilation, with a structure comprising juxtaposed angular sectors made of a second material the coefficient of expansion of which is higher than that of the first material.
The first and second materials can be selected respectively from among materials with lower coefficients of expansion, such as TA6V and titanium alloys, INC0909, TiAL or similar intermetallics with an average coefficient of linear expansion lower than 10.10xe2x88x926 m per degree Celsius; and from among materials with higher coefficients of expansion, such as INC0718 or similar nickel-based alloys, RENE77 and derivatives with an average coefficient of linear expansion of approximately 15.10xe2x88x926 m per degree Celsius.